Such lighting armatures are known per se. Sometimes these lighting armatures are also called light armature or light generator. They are used, inter alia, for general lighting purposes, for so-called sign and contour illumination, and for signal illumination, such as in traffic lights or traffic-control systems, for example in road-marking systems for dynamically or statically controlling traffic flows. Such light generators are further used in projection illumination and in fiber-optical illumination.
A lighting armature of the type mentioned above is known from U.S. Pat. No. 6,402,347-B1. The known lighting armature is provided with a LED light source having a luminous flux of at least 5 lm during operation and a plastic optical lens system for directing the radiation to be generated by the light source.
According to U.S. Pat. No. 6,402,347-B1, the possibility for the use of an optical system made from a synthetic resin material is based on the recognition that light-emitting diodes (LEDs) generate much less radiation heat and/or UV light than conventional light sources such as gas discharge lamps or halogen lamps. Since the LEDs can be chosen such that they emit little or no UV and/or IR-radiation, LEDs are eminently suitable for use in light engines. A further advantage of the use of LEDs is the compactness of such light sources. This advantage is used in practice to combine a plurality of LEDs in the lamp source and/or to make even more compact lighting armatures. These advantages could be useful for making compact lighting armatures with a plurality of LEDs for household and office lighting applications, wherein the housing not only functions as a cover for the electronic parts, but also can be given a decorative function. Although it is mentioned in U.S. Pat. No. 6,402,347-B1 that in principle, it is also possible to arrange the drive electronics outside the housing, it is to be noted that for household and office lighting applications the drive electronics generally will have to be incorporated in the housing.
A problem with electronic lamps, comprising electronic parts for controlling the light source, and in particular with multi-LED solid state lamps, is that the light source produces heat, which, if not adequately removed affects the performance of the light source and/or of the electronic parts, and as an effect thereof, the control of the light source and the light production is interfered with, and the lifetime of the light source is reduced.
Although, as stated in U.S. Pat. No. 6,402,347-B1, the heat emitted by a single LED is limited, in a multi LED system this heat can be sufficient to heat the LEDs and the drive electronics and thereby affect the performance of the light source driven by the drive electronics. This is particularly the case with multi-LED light sources comprised in compacted lighting armatures. Moreover, in electronic lamps wherein the housing is designed as a shell, such as a tubular hull made of metal, e.g. aluminum or steel, the heat removal is too low. To limit heating of the parts comprised by the housing, the known lighting armature of U.S. Pat. No. 6,402,347-B1 comprises a metal housing provided with cooling fins, or comprises means to apply forced air cooling, for example a fan incorporated in the housing by which an air stream can be generated. In the latter case the housing can be made of a synthetic resin.
A disadvantage of the known lighting armature is that incorporation of a fan makes the construction of the lighting armature more complex, apart from the fact that in compacted lighting armatures there is often no space for such a fan. A disadvantage of the metal housing with cooling fins is that such a housing is difficult to produce and thereby expensive, heavy in weight and, most importantly, introduces the risk of short circuitry and dielectrical breakdown. This problem is becoming even more critical since the lighting armatures with multi/LED systems could do a great job for domestic lighting purposes as well, but therefore have to comply with stringent norms on safety including high threshold values for dielectric breakdown.
The aim of the invention is to provide an electronic lamp, which does not have the said problems, or at least in lesser extent. More particularly, the aim of the invention is to provide a lighting armature, that is suitable for domestic lighting purposes which has improved balance in heat management properties and weight, no internal forced air cooling needs to be applied and higher security levels can be obtained.
This aim is has been achieved with the lighting armature according to the invention, wherein the housing has cooling fins made of a plastic composition having an orientation averaged thermal conductivity of at least 2.0 W/m·K.
The effects of the lighting armature according to the invention, having said cooling fins are that the threshold values for short circuitry and dielectric breakdown are increased compared to a corresponding lighting armature made of metal. Moreover, already by using cooling fins made of a polymer composition with such a low thermal conductivity, a substantially heat reduction can be achieved that internal forced air cooling can be dispensed with and weight can be saved. The plastic cooling fins also attribute to the safety aspects of the lighting armature in that these allow the lighting armature to be handled by touching the cooling fins rather than the electrically conductive metal shield.